The present disclosure relates to systems and methods for process control, and more particularly, to control processes related to pump flow rates.
Production of hydrocarbons form subterranean formations involves the design and use of complex fluid systems. For example, during the drilling of a hydrocarbon-producing well, drilling fluids (often called drilling muds) suspend and remove cuttings and lubricate the drill bit. During the drilling operation, it may also be necessary to alter the fluid, such as to seal off non-producing permeable formation regions or to minimize formation damage in the producing zones. Similarly, during a fracturing operation, the fracturing fluid is generally placed in stages such that the initial fluid is solids-free, followed by stages with various sizes and/or types of proppant. Thus, in these and other subterranean operations, it is often necessary to carefully control the system that creates the fluid to be sent down hole.
An automated system may be implemented to control the flow rate of pumps that supply the various components to the designed fluid and to monitor sensors in order to create a fluid having the desired ratio or concentration of components. Unfortunately, due to natural occurrences such as exposure to extreme temperatures and wear and tear on the machinery (e.g., additive pump impellers dulling or breaking), the actual flow rate of the additive pumps may not equal the desired flow rate (i.e., the setpoint) necessary for the proper solution concentration. To counteract this issue, the system may include a “feedback” or closed-loop control algorithm, wherein parameters such as the component pump flow rate may be monitored and continually incorporated by the control system in determining the necessary flow rate or quantity of additive still required to form the predetermined concentration.
However, even with a finely tuned control system, there may be a time delay between when a component setpoint is changed and when the component pump actually achieves a desired flow rate at the new setpoint value. This delay may be, for example, 30 to 60 seconds. In the past, the time between setpoint changes (i.e., a “stage” in the fracking process) may be a few minutes or hours, thus the pump delay of 30 to 60 seconds may be a small percentage of the overall stage time and may not have been job critical. However, current fracking jobs may require shorter stage times, for example of 15 to 30 seconds. Therefore, the delay duration may be unacceptable.